The Potter Group, Caltech

The Potter group, at the California Institute of Technology, is developing techniques for the study of neural cell cultures in vitro. Led by Dr Steve Potter, the group has pioneered technologies for the electrical linking of neurons in a petri dish to a computer. The computer is able to electrically stimulate the cells and to record their responses. By analysing the reactions of his cells to specific stimuli Potter is trying to understand the language used in neural communication. Also, by studying morphological changes in the neurons he is aiming to understand how these are related to learning and memory.

Multi-Electrode Array (MEA) culture dishes:
Central to Potter's work are culture dishes fitted with an array of micro-electrodes. A thin layer of hundreds, or thousands, of dissociated neurons are grown over the top of these electrodes (see image above). Neurons taken from rat embryos are used because they grow rapidly and spontaneously develop synapses and patterns of activity. The cultures can also survive for weeks, even months, at a time.

The dishes are made from glass and contain 61 transparent indium-tin oxide electrodes. The electrodes are spaced 70µm apart. The leads are insulated with silicon nitride whilst the electrodes themselves are plated with platinum black.

Potter calls this set-up an "animat", short for "artificial animal". This is because the computer is used to simulate a body whilst the neurons act as the brain. The communication between the cultured neurons and the simulated body is 2-way and works in real time. As the cells are stimulated they are seen to actually learn. The culture begins to understand that stimulus X is associated with stimulus Y.

Neuron Imaging:
One of the neuron imaging techniques used at this reasearch lab is 2-photon microscopy. This exotic microscope uses infrared lasers to illuminate and focus deep within a specimen. The team have also designed and built a high speed camera for time-lapse imaging of neurons stained with voltage sensitive dyes.

Using both of these technologies it can be seen just how neural cells organise themselves. Neurons tend to get bigger and more branched as they get older. This growth or pruning of axons or dendrites and changes in number of synapses is witnessed.

Links:
The Potter Group, Caltech: http://www.caltech.edu/~pinelab/PotterGroup.htm